A heater core transfers heat from a 1994 Ford Ranger's engine to the passenger compartment by running hot radiator coolant through a serpentine of tubing. Air blows past the hot fins of the heater core and into the truck cab.
The hoses running to and from the heater core must be removed from the engine compartment, but the core itself is accessed from inside the passenger compartment, on the driver's side next to the center console.
Turn off the engine, open the hood and remove the battery cable from the negative terminal. Make sure the engine is cool.
Attach a 3/8-inch interior diameter hose to the drain outlet on the bottom rear corner of the radiator on the driver's side, and place the bottom end in a resealable plastic container. Turn the drain valve (located above the drain outlet) counterclockwise with a pair of pliers. Drain the engine coolant into the resealable container, then close the valve by turning it clockwise. Remove the hose from the outlet.
Loosen the hose clamps on the radiator hoses where they attach to the heater core on the firewall. Remove the hoses.
Unscrew the screws holding the underdash cover in place on the driver's side of the passenger compartment. Remove the underdash cover.
Unscrew the four screws on the cylindrical heater core access cover and remove it. Remove the heater core by pulling it down and toward the rear of the vehicle. Replace the unit with a new heater core.
Reinstall the heater core access cover and screw in the retaining screws. Replace the underdash cover and screw it into place.
Replace the radiator hoses on the heater core in the engine compartment. Tighten the hose clamps. Add coolant until the level is between the minimum and maximum marks on the reservoir.
Replace the battery cable and start the engine. Check the system for leaks.
